Sound recording



Patented July 18, 1939 UNlTED STATES PATENT OFF'CE SOUND RECORDING` Waffe Application June 2 6, 1937, Serial No. 150,515.

11 Claims.

The present invention pertains to sound recording and, more particularly, to sound recording by the use of a galvanometer for the purpose of producing photophonographic sound records with a minimum of ground noise. It was proposed in Kellogg patent, No. 1,740,406, to record variable area sound records by the use of a galvanometer moving along a line parallel with the axis of movement of the sound record which galvanometer directed a triangular beam of light upon a narrow slit. It was further proposed in my application Serial No. 610,302, flled May, 9, 1932, now Patent No. 2,093,423, Sept. 21, 1937, to apply the same method to the production of push-pull sound records, i. e., sound records having complementary sound waves on the several halves of the sound track. It was also proposed in my application Serial No. 137,905, filed April 20, 1937, to use a plurality of complementary triangles in the light aperture in order to record a negative sound track from which a positive sound track having ground noise reduction could be printed.

An application of Karl Schwarz, Serial No. 139,850, filed April 30, 1937, discloses that the aperture defining the configuration of the light beam upon the slit may advantageously be made of variable contour. In this Schwarz application, it was proposed to use a pair of leaves movable about a pivot to change the configuration of a V-shaped aperture.

I have discovered that, if the movable leaf or shutter of such an aperture is pivoted at its middle point, it is possible to produce either volume expansion, volume compression or ground noise reduction without the introduction of eX- traneous sound. The present invention perrtains to apparatus for and methods of the application of the aforesaid discovery to the production of sound records.

One object of my invention is to provide a method of, and apparatus for, producing ground noise reduction without the introduction of eX- traneous noises.

Another object of my invention is to provide a novel means for providing volume compression or expansion either in the recording or reproducing of sound records.

Another object of my invention is to provide an improved shutter arrangement whichY will change the shape of the light aperture without affecting the total quantity of light transmitted thereby.

Other and incidental objects of my invention will be apparent to those skilled in the art by a reading of the following specication and an inspection of the accompanying drawing wherein Figure 1 is a perspective view of a sound recorder including a schematic diagram of the circuit thereof,

Figure 2 is an elevation of the improved shutter mechanism as applied to the aperture plate of Fig. 1, and

Figure 3 is an elevation of the improved shutter arrangement as applied to a somewhat dif- 10` ferent form of aperture plate.

Referring to Fig. 1, the usual exciter lamp is indicated at I, from which light is transmitted through the condenser lens 2 to the aperture plate 3, hereinafter described in greater detail. 15

From the aperture plate 3 the light is transmitted through the lens 4 to the galvanometer mirror 5, which reflects it through the lens 6 to the light slit plate 1 whereon an image of the apertures in the aperture plate 3 is formed by 20-l the lenses d'and 6. Light from these images, indicated at 8 andV 9, is transmitted through the slit I0 in the plate l, and is focused by the objective Il upon the photographically sensitive lm I2 for recording the sound record.

When the mirror 5 isy vibrated in accordance with the sound impulses to be recorded, the aperture images 8 and 9 are correspondingly vibrated across the slit IIJ, causing an increase or decrease in the respective areas intercepted, and thereby producing a push-pull sound record, as described in my aforesaid Patent 2,093,423.

The sound impulses to be recorded are applied to the translating'device I3 which may be any source of electric impulses, such as a microphone, a phonograph pick-up, a telegraphone, the outputof a radio receiver, etc; The output from this sound to audio current translating device is fed to the amplifier I4 where it is arnpliiied and passed to the galvanometer winding I5', whichv serves to vibrate the mirror 5 in accordance with the audio frequency impulses. A portion of the output from the amplifier i4 is transmitted to the bias amplifier I5, where this portion of the output is amplified, rectified and 45 iiltered to produce a pulsating uni-directional current corresponding to the envelope of the sound waves or the volume of the sound in the manner described, for example, in McDowell Patent No. 1,855,197. The output from this amplifier is passedthrough a coil IE, which serves to actuate a pair of shutters 21 and 28, as described and claimed in the copending application of J. O. Baker, Serial No. 82,375, filed-May 28, 1936 for the purpose of limiting the'exposure 55- area to the amount actually used in recording the particular sound impulses as described and claimed in the aforesaid McDowell patent. A portion of the output from the amplier I 6 is also passed through the coil I1 which may be connected in series with the coil I6, as indicated, or connected to the bias amplier I5 in any other desired manner and which serves to actuate the movable shutters I8 and I9 pivoted to the aperture plate 3.

It should be noted that these shutters are pivoted at their middle points, as indicated at 2!) and 2|, Fig. 2, and that, therefore, when they are rotated about their pivots, one end tends to close the aperture, while the other end tends to open it, and the total quantity of light passing through the respective triangular apertures 22 and 23 is thereby caused to remain' constant. It will be apparent that if the pull rod 24 is caused to move downwardly by the magnet l1, the slope of the shutters I8 and I9, and therefore the slope of the hypotenuses of the triangular im.- ages 8 and E! will be increased, while at the same time the shutters 21 and 28 will be opened. When ,the bias amplifier is so connected that this is done in response to an increase in the amplitude of the sound, the shutters 21 and 23 are opened suiciently to allow for the increased amplitude, While at the same time the increased slope of the shutters will cause a decrease in the proportionate amplitude of the record. Otherwise stated, the shutters I8 and I9 will compress the volume of the recorded sound impulses. Likewise, if the amplitude of the sound is decreased,

,the shutters 21 and 28 will move inwardly, the

rod 24 will move outwardly, the shutters I8 and I9 will move into a more nearly horizontal position, and increased sensitivity of the apparatus will result as the amplitude decreases, thereby compressing the volume of the recorded sound.

If it is desired to expand the volume of the recorded sound, all that is necessary is to reverse the connections to the bias amplier from the amplifier I4 and to move the solenoid I6 to the opposite side of the arm which it actuates; or the bias amplifier and the solenoid IB may be left as shown and the solenoid I'l may be connected to actuate the opposite ends of the shutters I8 and I9 in the same direction as illustrated; or the solenoid I1 may be left in its illustrated position and the rod 24 extended so that the core of the solenoid lies below, instead of above, it. If either of these changes isI made, then an increase in input from the translating device I3 will cause the shutters I8 and I9 to move to a position more nearly parallel to the slit I0, while a decrease in amplitude will cause them to move to a position more nearly transverse to the slit Il! and Volume expansion will result. The action of the ground noise reduction shutters 2T and 28 will, of course, remain as before.

The apparatus as above described is intended for what is known as class A push-pull record- .ing with ground noise reduction. In that type of recording, as will be apparent from an inspection of the apparatus just described, two similar sound records are produced, one on each half of the sound track area, these records being out of phase and. the portion of the sound track area not used in the sound record being obscured by the shutters.

If it is desired to use the improved apparatus of my invention to produce a bilateral sound :track wherein the wave images on the two halves of the sound track are in phase so that the sound track can he reproduced on an ordinary single photocell reproducer as distinguished from the push-pull reproducer necessary for the sound track above described, the form of aperture shown in Fig. 3 may be used. This aperture and the use thereof are, in general, the same as described in the aforesaid Baker application, Serial No. 82,375, distinguishing therefrom, however, in that shutters It and I9 are provided to change the configuration of the sloping edges of the aperture. In this arrangement, the rod 24 is connected by appropriate lengths to either the inner ends or the outer ends of the shutters I8 and I9, instead of being connected to either the left hand ends or the right hand ends of the shutters in the species of the invention shown in Fig, l. It will be apparent that since in this sound track both halves are to be identical, the action of the shutters will be correspondingly the same as in Fig. l, increasing the slope of the aperture on both sides simultaneously on increasing amplitude and decreasing it on decreasing amplitude, if volume compression is to be secured, or the reverse if volume expansion is to be produced.

It will be apparent to those skilled in the art that my invention is not limited to the specific forms thereof shown in the drawing, but that the improved centrally pivoted shutters, or one of them., may be used to advantage in connection with practically any type of aperture used in variable area recording to change the angular relation between one or more sides of the aperture and the other side or sides.

Having now described my invention, I claim:

1. Apparatus of the class described, including means for projecting an image of a light aperture upon a slit, means for moving said image in accordance with the impulses to be recorded, and .f

means for changing the shape of said image in accordance with the amplitude of said impulses while maintaining a substantially constant area of said image.

2. Apparatus of the class described, comprising means for projecting a triangular beam of light upon a narrow slit, and means for changing the angle of at least one side of said triangle in accordance with the amplitude of the sounds to be recorded without changing the area of said triangle.

3. Apparatus of the class described, comprising a pair of shutters movable about their middle points to dene the shape of a light beam, means for moving said shutters in accordance with the envelope of the sounds to be recorded, and means ier vibrating said light beam in accordance with the sounds to be recorded.

4. Apparatus of the class described, including means for projecting an image of a light aperture upon a slit, means for moving said image in accordance with sounds to be recorded, and means for varying the angular relation between the sides of said image in accordance with the amplitude of the sounds to be recorded without changing the area of said image.

5. Apparatus of the class described, comprising means for projecting a triangular beam of light upon a narrow slit, and means for changing the angular relation between the sides of said image in accordance with the amplitude of the sounds to be recorded without changing the area of said image.

6. Apparatus of the class described, comprising a pair of shutters movable about their middle points to dene the shape of a light beam, means for changing the angular relation between the edges of said shutters in accordance with the envelope of the sounds to be recorded, and means for vibrating said light beam in accordance with the sounds to be recorded.

7. Apparatus of the class described, comprising means for projecting a pair of triangular beams of light upon a narrow slit, and means for changing the angle of at least one side of each of said triangles in accordance with the amplitude of the sounds to be recorded Without changing the area of said triangles.

8. Apparatus of the class described, comprising a pair of shutters movable about their middle points to define the shape of a pair of light beams, means for moving said shutters in accordance with the envelope of the sounds to be recorded, and means for vibrating said pair of light beams in accordance with the sounds to be recorded.

9. Apparatus of the class described, including means for projectingimages of a pair of light apertures of complementary conguration upon a slit, means for moving said images in accordance with sounds to be recorded, and means for varying the angular-relation between the sides of said images in accordance with the the amplitude ci the sounds to be recorded without changing the area of said images.

l0. Apparatus of the class described, comprising means for projecting a pair of oppos-itely oriented triangular beams of light upon a narrow slit, and means for changing the angular relation obetween the sides of said images in accordance with the amplitude of the sounds to be recorded without changing the area of said images.

l1. Apparatus of the class described, comprising an aperture plate having a pair of oppositely directed triangular apertures, a pair of shutters movable about their middle points in relation to said plate to vary the shape of a pair of light beams, and means for changing the angular relation between the edges of said shutters and said apertures in accordance with the amplitude of the sounds to be recorded.

GLENN L. DIMMICK. 

